Isn’t the main point about the lowly chain that it’s efficient?
When clean, yes. When covered in mud, less so*. I certainly notice no reduction in drive efficiency over a derailleur system when riding my Rohloff-equipped bike. In theory, the spur-gear design of the pinion should be measurably (but probably not detectably by the rider) more efficient than the epicyclic design of an IHG, but who knows? It should also be stronger than an equivalent epicyclic, but it would have to be as it’s being pedalled directly (with no step-up between chairing and sprocket to reduce the torque load).
So, nobody knows of any reliability figures, then? Depending on sale volumes, that’s probably a good sign. I’m sure we’d get to hear about any major issues fairly quickly in such a high value component! 😉
*mostly, though, I hate the constant cleaning a derailleur needs, and grinding noises whenever you shift under load. For me, an internal gear arrangement is all about low-maintenance, reliable, fuss free shifting. YMMV.